This invention relates to radio tuners, and more particularly to a tuning indicating device in a tuner employed in a radio receiver.
A conventional tuning indicating device in an FM tuner employs a pointer indication type signal strength meter (hereinafter referred to as "an S-meter" when applicable) and a pointer indication type center tuning meter (hereinafter referred to as "a T-meter" when applicable). In order to operate the S-meter, an intermediate frequency signal component derived from the IF stage is rectified to supply a rectified current to the S-meter. The pointer of the S-meter indicates the electric field strength. Therefore, a maximum deflection of the pointer indicates a best signal receiving condition. However, the S-meter suffers from a disadvantage that if the input is greater than that with which the limiter circuit operates satisfactorily, it is difficult to clearly obtain the maximum deflection point, that is, the best signal receiving condition. In order to overcome this difficulty, the high-grade radio receiver employs the aforementioned T-meter in combination with the S-meter to obtain the best signal receiving condition. The T-meter utilizes the S-figure characteristic which is obtained from the ratio detector. If the voltage of the S-figure characteristic is read with the T-meter and the central frequency of the received signal is set to the center of the S-figure where the voltage is at zero, the signal reception can be achieved with the best S/N ratio, the minimum distortion, the maximum output, and the best separation. When the S-meter and the T-meter are employed in combination, the arrangement of these meters is as indicated by reference numerals 1 and 2 in FIG. 1.
However, this tuning indicating device is still disadvantageous in that (1) it is necessary to provide two meters, (2) it is necessary to read the two meters, and (3) the meters are liable to become out of order because they are electro-mechanical meters. In order to overcome the above-described difficulties (1) and (2), a method has been proposed in which the S-meter and the T-meter are provided in one casing 3 as indicated in FIG. 2. However, it is difficult to completely overcome the above-described difficulties because the arrangement of the meter shown in FIG. 2 is fundamentally similar to that of the two meter system.